Home » Public Forums » GMCnet » Is this Low engine vacuum?
| Is this Low engine vacuum? [message #146625] |
Sat, 15 October 2011 18:50  |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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I have a pretty freshly rebuilt ( last year) 455, it was bored .030 over and uses a Jim bounds cam.
I'm trying to get it to use a normal amount if fuel (8 to 10 mpg)
I bought a Wide band O2 sensor, LC1, and redid the exhaust with 3" pipe. I'm getting about 14AFR at cruise and lower when I step on it
At idle in drive I'm getting 15" of vacuum with a little needle shake. I was expecting closer to 20 and a smooth needle, but am hoping Jims cam lowers it?
Timing should correct, I'm going to check it tomorrow.
Idle speed is ~700 rpm
Does this vacuum see right for a Jim bounds cammed engine??
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] Is this Low engine vacuum? [message #146635 is a reply to message #146625] |
Sat, 15 October 2011 20:01  |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
Karma: 0
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Senior Member |
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I've got a '73 230 with a dead stock motor (85K miles)
I see 14-16" vacuum at a steady cruise (60-65mph)
7.5 - 8.5mpg, towing vs not. Sometimes I'll see 9mpg on a long, flat
run. Got 10.1 with a big tailwind once!
I really want that 12-13mpg that so many of you are getting. I just
don't think the physics are the same here on the Left Coast...
Kelvin
'73 23' in Eugene, OR
>
>
> I have a pretty freshly rebuilt ( last year) 455, it was bored .030 over and uses a Jim bounds cam.
>
> I'm trying to get it to use a normal amount if fuel (8 to 10 mpg)
> I bought a Wide band O2 sensor, LC1, and redid the exhaust with 3" pipe. I'm getting about 14AFR at cruise and lower when I step on it
>
> At idle in drive I'm getting 15" of vacuum with a little needle shake. I was expecting closer to 20 and a smooth needle, but am hoping Jims cam lowers it?
>
> Timing should correct, I'm going to check it tomorrow.
> Idle speed is ~700 rpm
>
> Does this vacuum see right for a Jim bounds cammed engine??
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| Re: [GMCnet] Is this Low engine vacuum? [message #146640 is a reply to message #146635] |
Sat, 15 October 2011 20:29 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Kelvin, I just got back from GMCWS and points south. I installed a newly
rebuilt Manny T transmission and a final drive that I set up using Jim Ks
3:70 Gears. I drove over 3100 miles with my 78 Royale with a bone stock 403.
Flat & level vacuum runs about 10 or 11 inches of mercury at 3200 RPM about
72 or 3 MPH. I drove over the Siskiou summit twice and the grapevine twice.
Ran the dash air most of the time. I used 301 Gallons of 87 Octane. The 26
foot Royale loaded like I do scales in about 10000 pounds. Like Gene Fisher
says GMCs get about 8 to 10 mpg. When I keep the speed down to 55, the
mileage goes up to 11 or so, but I am bored stiff. To quote Sammy Hagar, "I
can't drive 55". Maybe the difference in fuel economy between East vs West
is that they travel East/West and we travel North/South. <grin>
On Sat, Oct 15, 2011 at 6:01 PM, Kelvin Dietz <kelvin@datsuns.com> wrote:
> I've got a '73 230 with a dead stock motor (85K miles)
>
> I see 14-16" vacuum at a steady cruise (60-65mph)
>
> 7.5 - 8.5mpg, towing vs not. Sometimes I'll see 9mpg on a long, flat
> run. Got 10.1 with a big tailwind once!
>
> I really want that 12-13mpg that so many of you are getting. I just
> don't think the physics are the same here on the Left Coast...
>
> Kelvin
> '73 23' in Eugene, OR
> >
> >
> > I have a pretty freshly rebuilt ( last year) 455, it was bored .030 over
> and uses a Jim bounds cam.
> >
> > I'm trying to get it to use a normal amount if fuel (8 to 10 mpg)
> > I bought a Wide band O2 sensor, LC1, and redid the exhaust with 3" pipe.
> I'm getting about 14AFR at cruise and lower when I step on it
> >
> > At idle in drive I'm getting 15" of vacuum with a little needle shake. I
> was expecting closer to 20 and a smooth needle, but am hoping Jims cam
> lowers it?
> >
> > Timing should correct, I'm going to check it tomorrow.
> > Idle speed is ~700 rpm
> >
> > Does this vacuum see right for a Jim bounds cammed engine??
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: Is this Low engine vacuum? [message #146645 is a reply to message #146625] |
Sat, 15 October 2011 20:57 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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My vacuum reads low also. As it turns out my gage reads about 3"
lower then others I have checked it against. That could be your problem but it should be pretty steady. Also when you have more miles on the engine things will most likely seat in better.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Is this Low engine vacuum? [message #146681 is a reply to message #146635] |
Sun, 16 October 2011 09:57 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Remember, I calimed 12 from Asheville to Braselton. All freeway, all at 55 cruise, all downhill, decent gas without alcohol, and it's a 23' coach with Thorley headers and 3 inch exhaust, mild temp, new vacuum lines and air filter element. IOW as good as it will ever get. In normal use (A/C on, 60-65 MPH cruise) it does around 10 give or take a tenth or two. If I'm running late to make a show site, it doesn't do so well.
--johnny
________________________________
From: Kelvin Dietz <kelvin@datsuns.com>
To: gmclist@temp.gmcnet.org
Sent: Saturday, October 15, 2011 9:01 PM
Subject: Re: [GMCnet] Is this Low engine vacuum?
I've got a '73 230 with a dead stock motor (85K miles)
I see 14-16" vacuum at a steady cruise (60-65mph)
7.5 - 8.5mpg, towing vs not. Sometimes I'll see 9mpg on a long, flat
run. Got 10.1 with a big tailwind once!
I really want that 12-13mpg that so many of you are getting. I just
don't think the physics are the same here on the Left Coast...
Kelvin
'73 23' in Eugene, OR
>
>
> I have a pretty freshly rebuilt ( last year) 455, it was bored .030 over and uses a Jim bounds cam.
>
> I'm trying to get it to use a normal amount if fuel (8 to 10 mpg)
> I bought a Wide band O2 sensor, LC1, and redid the exhaust with 3" pipe. I'm getting about 14AFR at cruise and lower when I step on it
>
> At idle in drive I'm getting 15" of vacuum with a little needle shake. I was expecting closer to 20 and a smooth needle, but am hoping Jims cam lowers it?
>
> Timing should correct, I'm going to check it tomorrow.
> Idle speed is ~700 rpm
>
> Does this vacuum see right for a Jim bounds cammed engine??
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Is this Low engine vacuum? [message #146690 is a reply to message #146625] |
Sun, 16 October 2011 11:36 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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| Keith V wrote on Sat, 15 October 2011 18:50 |
I have a pretty freshly rebuilt ( last year) 455, it was bored .030 over and uses a Jim bounds cam.
I'm trying to get it to use a normal amount if fuel (8 to 10 mpg)
I bought a Wide band O2 sensor, LC1, and redid the exhaust with 3" pipe. I'm getting about 14AFR at cruise and lower when I step on it
At idle in drive I'm getting 15" of vacuum with a little needle shake. I was expecting closer to 20 and a smooth needle, but am hoping Jims cam lowers it?
Timing should correct, I'm going to check it tomorrow.
Idle speed is ~700 rpm
Does this vacuum see right for a Jim bounds cammed engine??
|
No thoughts on this??
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] Is this Low engine vacuum? [message #146694 is a reply to message #146690] |
Sun, 16 October 2011 11:43 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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At sea level, you should be pulling 17plus of Vac. at idle.
Check and see if you can advance the timing.
On Sun, Oct 16, 2011 at 9:36 AM, Keith V <my427v8@hotmail.com> wrote:
>
>
> Keith V wrote on Sat, 15 October 2011 18:50
>> I have a pretty freshly rebuilt ( last year) 455, it was bored .030 over and uses a Jim bounds cam.
>>
>> I'm trying to get it to use a normal amount if fuel (8 to 10 mpg)
>> I bought a Wide band O2 sensor, LC1, and redid the exhaust with 3" pipe. I'm getting about 14AFR at cruise and lower when I step on it
>>
>> At idle in drive I'm getting 15" of vacuum with a little needle shake. I was expecting closer to 20 and a smooth needle, but am hoping Jims cam lowers it?
>>
>> Timing should correct, I'm going to check it tomorrow.
>> Idle speed is ~700 rpm
>>
>> Does this vacuum see right for a Jim bounds cammed engine??
>
>
>
> No thoughts on this??
> --
> Keith
> 69 Vette
> 29 Dodge
> 75 Royale GMC
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: Is this Low engine vacuum? [message #146731 is a reply to message #146625] |
Sun, 16 October 2011 20:03 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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well used a better gauge with more resolution;
at idle in park I get 17
in drive I get 16
timing was at 8
No vacuum leaks to be found
I guess I'm ok
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: Is this Low engine vacuum? [message #147048 is a reply to message #146625] |
Wed, 19 October 2011 11:24 |
philipswanson
Messages: 282
Registered: January 2004
Karma: 0
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Senior Member |
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Get the card for the cam and note the duration of that cam. A higher duration and/or overlap will sometimes cause the vacuum to be much lower. No such thing as a Jim Bounds cam, read the specs. Check the card and call Competition Cams tech line. If it is still low, check for vacuum leaks, especially the intake like Jim K. says.
Phil Swanson
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